I tried it once, and it really didn't work

Sail was way under outhauled, felt like a sack of potatoes

If you were stranded on a desert island, with only that equipment available, and you needed to escape into the wild blue yonder and rescue yourself, then...
Under downhaul the sail. This will mean you'll need less boom length, so you might just be able to get enough outhaul on the sail to make it manageable. Perhaps. Enough to escape the island, anyway